A　simple,　easy-to-use　approximate　equation,　in　the　form　of　a　normal　probability　distribution　function,　was　derived　and　proposed　for　breakthrough　curves　of　fixed　bed　reactors　and　adsorbers.　The　equation　predicts　breakthrough　curves　and　evolution　in　time　of　concentration　and　temperature　distribution　in　fixed　beds　with　an　accuracy　higher　than　or　comparable　to　the　best　of　the　other　equations　previously　proposed.